1. Field of the Invention
The invention pertains to the field of methods of production of plastic containers, and containers produced by such methods. More particularly, the invention pertains to methods of production of plastic containers which are resistant to organic liquids and hydrocarbons such as gasoline, and containers produced by these methods.
2. Description of Related Art
Gasoline is liable to permeate out of its container. Current gasoline containers such as, for example, the common storage container and oil boxes used in a car, motor, mower, and the like, are mostly produced from material composed of high density polyethylene (HDPE) having low cost but excellent processability, as well as physical and chemical properties.
Unfortunately, HDPE containers, when used for storing gasoline, are subject to serious gasoline permeation that results in problems associated with environmental protection and public health, as well as a great loss of resources. Recently, various approaches have been used successfully for improving resistance of gasoline permeation, for example, by using HDPE that has been subjected to surface fluorination (J. P Hobbs., M. Anand. And B. A. Campion, in Barrier Polymer and Structures, W. J. Koros Ed., Chapter 15, American Chemical Society, Washington (1990)) or sulfonation (W. E. Walles, in Barrier Polymer and Structures, W. J. Koros Ed., Chapter 14, American Chemical Society Washington (1990)), or using a multi-layer co-extrusion/laminar blend blow-molding process (S. Willian, Chemtech August 481 (1988)).
However, surface treatment approaches may have several disadvantages such as process risk, high pollution, high investment or difficulty in recycling the waste. On the other hand, multi-layer co-extrusion method has disadvantages of complicates in the blow-molding machine, high capital investment, and difficulty in recycling the waste. On contrary to the above-mentioned two processes, in addition to the absence of the above-described disadvantages, the laminar blend blow-molding has advantages as simple processing in that a traditional PE blow-molding machine can be used, capability of recycling and re-use of the waste, as well as lower investment over the above-mentioned two processes. Therefore, the laminar blend blow-molding technique has attracted the interest of the container manufacturer and is developing rapidly in recent years.
Nevertheless, the technical level of the laminar blend blow-molding is very high in that the parallel distribution of the growing polyamide laminar must be controlled effectively, and that, at present, it can be carried out only through using a special designed and expensive patented blow-molding machine from Dupont. The concept of lamination blow molding has been disclosed in a few patents such as ROC Pat. No. 53,999(1992) as well as U.S. Pat. No. 4,416,942 (1983) and U.S. Pat. No. 4,950,513 (1990). However, PA is incompatible with PE, and the interface adherence between them is poor, such that it is often necessary to incorporate CP into PE/PA during the processing to increase the interface adherence of PA to HDPE.
Polyolefin has characteristics of low cost, low weight, good environmental stress cracking, excellent compact resistance, low moisture absorption, easy processability and flexibility in product designing. It thus becomes the most commonly used packaging materials. However, when used for packaging organic liquids and vapors, it has often suffered from its low permeation resistance.
Various prior art techniques for improving the permeation resistance of the polyolefin has been proposed, such as those described in, for example, U.S. Pat. Nos. 2,811,468; 3,862,284; 3,998,180; 4,081,574; 4,142,032; 4,394,333; and 4,467,075, wherein processes for surface treating plastic film and container with fluorine or bromine gases to improve effectively permeation resistance with respect to the solvent but not to the vapor were disclosed.
Further, JK No.55-80439 disclosed a process for treating surface of polyolefin article with a fluorocarbon plasma; U.S. Pat. No. 4,182,457, JK No.59-103726 and JK No.59-103727 disclosed processes for co-extruding six-layer structure of polypropylene/adhesive layer/ethylene-vinyl alcohol copolymer/adhesive layer/regenerated material/polypropylene and then blow-molding by using ethylene-vinyl alcohol copolymer (EVOS) as the barrier layer, characterized in that the product thus produced can resist effectively the permeation of gas.
U.S. Pat. Nos. 3,857,754 and 3,975,463 disclosed production of a resistant 3-layer film by blending homogeneously a polyolefin, ethylene-vinyl alcohol copolymer and carboxylated thermoplastic resin with high shear equipment. As the technique to improve the permeation resistance of polyolefin with polyamide, U.S. Pat. No. 3,873,667 disclosed a method for improving a blend of polyolefin/polyamide by thermal treatment.
U.S. Pat. Nos. 3,373,222, 3,373,223 and 3,373,224 disclosed the use of a carboxylated polyethylene-unsaturated carboxylic acid copolymer as the dispersant for improving the barrier property and the mechanical strength. Unfortunately, these patents had emphasized on the technique for the preparation of homogeneous polyolefin/polyamide blend, and can not improve effectively the barrier property of the polyolefin.
U.S. Pat. Nos. 4,410,482, 4,416,942 and 4,444,817 disclosed a heterogeneous laminar blend that is composed of a polyamide distributed within a polyolefin matrix containing a compatibilizer, and is characterized in that it had a high permeation resistance to hydrocarbon compounds. The disadvantage thereof relied on that, since the preparation of said blend comprised a dry blend step of compositions, a special extrusion equipment must be used and further, high shear force and high energy should be avoided carefully to complete the melt procession.
ROC No. 53,999 disclosed the preparation of a modified polyamide by reacting extruding aliphatic polyamide and a semi-aromatic polyamide with compatibilizer in a conventional extrusion equipment, wherein a blend of polyamide/modifiedpolyamide was produced. Unfortunately, the degree of improvement for permeation resistance could not satisfy the requirement of the environmental protection law with respect to the leakage, and therefore was unfavorable to its commercial production.
In view of the forgoing, the inventor has done extensive study and finds that a PE/MPA blend bottle can be produced by selecting appropriate composition of CP and PA, preparing modified polyamide (MPA) using a twin-screw extruder, incorporating properly said MPA into PE and finally, producing said PE/MPA blend bottle using a conventional non-expensive blow-molding machine. The PE/MPA blend bottle thus produced can achieve a high gasoline permeation resistant effect that only less than 5 vol. % of the content will permeate out of the bottle after storing at 40xc2x0 C. for one year. This effect is several-fold higher than that achieved by prior art. Further, the process according to the invention can be carried out in a conventional cheap blow-molding machine instead of the patented one so that it has an advantage of low production cost.
The invention relates to a process for producing a high gasoline permeation resistant plastic blend container, comprising preparing a modified polyamide by modifying polyamide with a compatibilizer precursor and then laminar blend blow-molding using a cheap conventional blow-molding machine from a composition of a polyolefin incorporated with a modified polyamide (MPA) into a bottle. The invention relates further to a high gasoline permeation resistant container obtained according to the above-described process, characterized in that it consists of a MPA laminar structure within a HDPE matrix, and has a gasoline permeation resistance of less than 5 vol. % of the total gasoline content thereof after storage at 40xc2x0 C. for one year.